Layer-by-Layer Single-crystal Two-dimensional Material Growth by Geometric Confinement

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs) and their heterostructures have been widely studied for next-generation electronics. However, the following critical challenges have hindered them from their commercialization: 1) precise layer control during their growth, 2) maintaining single crystallinity at wafer-scale, and 3) inevitable transfer-process to fabricate heterostructure for various next-generation applications such as spintronics, valleytronics, and optoelectronics.

This thesis introduces a confined-growth technique that can overcome the aforementioned hurdles simultaneously by introducing a geometric SiO₂ mask that has growth selectivity from the underlying substrate. As micrometer-scale SiO₂ trenches reduce the growth duration substantially, single-domain WSe₂ and MoS₂ arrays are obtained on an arbitrary substrate at wafer-scale by filling the trenches before the second layer of nuclei is introduced, thus enabling layer-by-layer growth without requiring epitaxial seeding.

In addition, subsequent MoS₂ growth on the WSe₂ arrays yields MoS₂/WSe₂ heterostructures. Therefore, we for the first time demonstrate single-domain TMDs arrays and their heterostructures at wafer-scale with controllable thickness, which of performances are comparable to that fabricated from TMDs flake. This confined-growth technique not only can overcome key obstacles of 2D materials, but also provide a platform with great potential for next-generation 2D-material-based applications.